1. Field of the Invention
The present invention relates to liquid organic emulsion scintillators, and more particularly, to liquid organic emulsion scintillators which can be polymerized into solids for facile disposal.
2. Description of the Prior Art
A significant portion of low level radioactive wastes (radwastes) originate from non-fuel cycle sources, including medical and academic institutions. These institutional radwastes include organic liquid scintillation liquids (LSC cocktails) which present particular problems. One means for disposal of such radwastes is by burial in shallow trenches at commercial burial sites. Due to the limited number of such sites, radwastes are often transported over long distances for burial. The problems inherent in transporting such radwastes are well known, such as an accidental discharge resulting from an accident to the container, e.g. tank truck or tank car, transporting the liquid radwaste. An assessment of the problems of institutional radwaste disposal is made in R. Anderson et al., "A Preliminary Impact Assessment of Institutional Radioactive Waste Disposal", pp. 151-8 EPA 520/3-79-002 (1979).
At present, a preferred method used commercially to manage the problems of LSC cocktail radwaste transportation and disposal is mixing with adsorbents (at a loading ratio of up to 1:10 LSC cocktail to adsorbent) and then loading the combination into barrels for transportation to a disposal site. However, this alternative has at least two disadvantages. The first is that small institutions are at a disadvantage in that the wastes must either be shipped to an intermediate processing facility or stored until sufficient waste is accumulated to economically justify a separate shipment to a burial facility. The second disadvantage is the large amount of limited burial space which is used up when such a large volume of adsorbent must be used to dispose of LSC cocktail radwaste.
Other approaches to solving the problem of LSC cocktail radwaste have been suggested. For example, S. R. Sachen et al, Health Physics, 36, 67 (1970) describes a method for decontamination and recovery of 1,4 dioxane based liquid scintillator. Another suggestion for reducing the above problem is volume reduction of the waste by distillation as described in H. G. Claycamp et al., Health Physics, 34, 716 (1978) and S. Kojma et al., Radioisotopes, 28, 447-9 (1979). The possibility of incineration of waste liquid scintillation fluid is treated by R. W. Granlund in M. W. Carter et al, eds., Management of Low-Level Radioactive Waste, Vol. 1, p. 419, Pergamon Press, New York (1979). Each of the above possibilities has its own disadvantages which have hindered their wide scale development and use.
Because solids have advantages in terms of ease of handling during transportation and disposal, attention has been directed to reducing the problems described above. In addition to reductions in volume by distillation, other means of reducing the wastes to solid form have been pursued. One such avenue of purusit has been the addition of monomers such as polyurethane or epoxy resins to encapsulate concentrated wastes according to a method described in T. Kaneko et al., Radioisotopes, 28, 92-4 (1979). That article describes a process whereby the organic liquid and water are largely evaporated before resins are added to the remaining concentrate and the resins polymerized to encapsulate the radwaste. As set forth by the authors of that article, various problems remain in using their procedure, including adapting the polymer to the particular cocktail, and the incineration or other method used for disposal of the extracted solvents. The cost of the monomer resins must be taken into account. Moreover, as noted by the authors, the monomer resins are an added component and by their estimates, the pre-treatment weight and volume of LSC cocktail would be doubled by treating the LSC cocktail waste without first removing the volatile components of the cocktail. In addition, when such an encapsulation method is used, the volatile components are not solidified, but instead are only temporarily trapped and can be released unexpectedly, creating hazards of fire and the potential for exposure to toxic fumes for persons handling the waste.
While plastic scintillators are known in the prior art, there are a number of situations where they are not useful, e.g., when the sample is soluble only in aqueous solutions. Furthermore, plastic scintillators are typically not useful for counting low energy particles often used in tracer studies such as those emitted when tritium is the radiolabel.
Counting of biological fluids as gelled suspensions is described in Bollinger et al, Anal. Chem., 39, 1508 (1967). However, no system is presently available which counts as a fluid emulsion and can be subsequently solidified for disposal. Furthermore, in prior art systems, (1) the volume of waste for disposal is significantly increased during the treatment process or (2) additional steps are involved in the disposal process which many times generate other wastes, e.g. evaporated solvents, and (3) no solidification of the volatile solvents takes place, but rather such solvents are either encapsulated or absorbed.